Method of crown finishing the teeth of internal gears



D. w. DANIEL 2,864,282

METHOD OF CROWN FINISHING THE TEETH OF INTERNAL GEARS Dec. 16, 1958 4 SheetsSheet 1 Filed Nov. 8, 1954 INVENTOR. DAVID W.DANIEL BY W "I I I'll,

ATTORNEY Dec. 16, 1958 D. w. DANIEL METHOD OF CROWN FINISHING THE TEETH OF INTERNAL GEARS Filed Nov. 8, 1954 4 Sheets-Sheet 2 INVENTOR.

DAVID w. DANIEL ATTORNEYS Qom Dec. 16, 1958 D. w. DANIEL 8 METHOD OF CROWN FINISHING THE TEETH OF INTERNAL GEARS Filed Nov. 8, 1954 4 Sheets-Sheet 3 FIG.9.

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INVENTOR.

DAVID w. DANIEL ATTORNEYS Dec. 16, 1958 D w. DANIEL 2,864,282

METHOD OF CROWN FINISHING THE TEETH OF INTERNAL GEARS Filed Nov. 8, 1954 4 Sheets-Sheet 4 [II I FIG.|4.

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METHDD F CRQWN FHNEHHNG THE TEETH ()F INTERNAL'GEAR 4 Claims. (Cl. 90-16) The present invention relates to amethod of crown .finishing the teeth of an internal gear.

It is an object of the present invention to provide a method of finishing the teeth of an internal gear which permits using a single cutter or tool to produce different amounts of crown on identical gears.

More specifically, it is an object of the present invention to provide, a method of finishing internal gears to produce a crown on the teeth thereof by a method. which comprises selecting a direction of relative traverse between the cutter and gear to produce the required crown.

Ofher objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings, wherein:

Figure l is a diagrammatic front elevational view with parts in section, illustrating the relationship between a ring and a small cylinder received therein.

Figure 2 is a section on the line 22, Figure 1.

Figure 3 is a sectional view on the line.3-3, Figure 2.

Figure 4 is a sectional view on the line 44, Figure 2, the small cylinder being sectioned perpendicular to its axis.

Figure 5 is a fragmentary diagrammatic front elevational view showing successive positions ofa thin cylinder moved with respect to a ring.

Figure 6 is a sectional view on the line 6-6, Figure 5.

Figure 7 is a fragmentary diagrammatic elevational view showing successive positions of a thin cylinder moved relative to a ring in a direction oblique to the axes of both the ring and small cylinder.

Figure 8 is a sectional view on the line 8-8, Figure 7.

Figure 9 is a sectional view on the line 99, Figure 8,

showing the path traversed by the cylinder in its moveillustrating the configuration ofcrownedteeth provided on a cutting tool.

Figure .12 is a diagrammatic view illustrating the tooth contact relationship between teeth of an internal gear and the crowned teeth of a pinion in mesh therewith.

Figure 1:3 is a front elevational view of the gear shaving machine, adapted to carry out thepresentmethod.

Figure 14 is a fragmentary vertical sectional view through a portion of the machine illustrated in Figure 13. In order to describe the theoretical basis of the present invention, reference is made first to the surface contacting relationship between a ring and a small cylinder-contained therein. It will of course be appreciated that this contact'is analogous to the contactbetweenan internally toothed ring member ora gear on thevone hand and an externally toothed gear-or :pinion on; the

other hand.

2,864,282 Patented Dec. 16 1 958 Referringfirst to Figures 1-4 there is illustrated a ring R having an internal surface 10 of the illustrated configuration in contact with the external surface 12 of a cylinder C,,. It will be observed that the internal surface 10 of the ring has a minimum diameter between the ends thereof, this diameter being designated by the reference numeral 14 in Figure 2. On the other hand, the cylinder C is a true cylindrical body and in the present case it is assumed that it is in line contact with the surface 10 of the cylinder along the line designated by the numeral 16 in the figure. This line 16 is an axial element of the cylinder and is accordingly a straight line and represents the only instantaneous contact between the interior surface 10 of the ring R and the exterior surface of the cylinder C It will of course be obvious that the surface 10 might be produced "at the interior of the ring R,, by employing the cylinder C as a tool, such for example as a cutting or grinding tool, and moving it to the illustrated position from a position displaced inwardly toward the center of the ring from the illustrated position, while driving both the ring andthe cutter in rotation.

It will further be apparent that having brought the ring and the cylinder into the relationship illustrated in these figures, the cylinder C might be reciprocated in the direction of its axis without disturbing the illustrated relationship. If however, while the cylinder and rim were to continue to rotate, the ring R, were moved in the direction of its axis, further abrading or cutting thereof bythe cylinder C would occur. 7

it will further be apparent that the curvature which would be imparted to the surface lit-by the cylinder .C without reciprocation is a direct function of the angle between the axis of the ringand the axis of the cylinder.

Referring now to Figures 5 and 6 there is illustrated the relationship between a ring R and an extremely thin cylinder C whichmay be considered simplyas a circular disc. In these figures it will be observed that if the cylinder C is moved from the full line position through the intermediate position to the final dotted line position it will in etfect generate a surface equivalent to the surface .ofthe cylinder C Thus, if during. movement of the cylinder C fromthe full line to the dotted line positionthe ring R is rotated, its interior surface 20 will be curved as illustrated in Figure 6 tohave a minimum diameter-inithe. plane 22 midway between'the ends of the ring. g

From the foregoing it will be apparent that a ring such as R,, or R may have an interior surface thereof finished to the shape illustrated in the figures by one of two methods. In the first place, this surface maybe produced byemploying a tool in the formof a small cylinder having its axis inclined to theaxis of the ring and moved radially from thecentral portion of the ring into the material of thering until full contact is established between the ring and cylinder from end to end of the-ring or throughout theaxially overlaping portions thereof. Alternatively, the same identicalsurface may be produced. at'the interior of the ring by employing a disc or extremely thin cylinder having'its' axis-inclined to the axis of the ring at the same angle'asjthe angleof inclination of the. cylinder and byfeeding the'disc or thin cylinder C in' the direction of its axis, so long as its axisfoc- 1 cupies thepositionoftheaxis of the cylinder-C In both'the foregoing cases the crowned or curved interior surface of the cylinder dependsupon the angle betweenthe-axes of the ring and cylinder. This angle is designated :XA in the figures and is referred to as the crossed axes angle. fl

. Referring now :to Figures 7-9 there :is illustrated :a sring' R -having;arr-internalsurface 30. which is presumed to be generated by a disc or thin cylinder C In this tact would be at the ends of the teeth of the gear.

case it is assumed that the cylinder C is positioned in space with its axis extending at an angle XA with respect to the axis of the ring R In this case however, traverse of the small cylinder C relative to the ring R is not in the direction of the axis of the cylinder C but instead, is along a line designated T which in this instance is oblique with respect both to the axis of the ring R and the axis of the cylinder C It will be apparent that the relative traverre along the line T between the cylinder C and the ring R considering the cylinder C to be operating as a tool, and considering the ring R to be rotating sufficiently to produce a uniform machining action over its entire inner surface 30 by the cylinder C will produce a crowned surface having a minimum diameter in the plane 32 intermediate the ends of the cylinder. In this case however, the amount of curvature of the surface 30 as measured by deviation from a line 34 parallel to the axis of the ring R is a function of the angle between the line of relative traverse T and the axis of the ring R This angle is designated in Figure 8 as TA and is referred to herein as the traverse angle.

In the foregoing simplified examples reference is made to smooth surfaced rings and cylinders, whereas the present invention relates to the finishing of the teeth of an internal gear. To continue the analogy the small cylinder C to C according to the present invention is a small toothed pinion having teeth shaped to mesh with the internal teeth of the internal gear. Accordingly, for any particular gear, the crossed axes angle XA which is the angle in space between the axis of the gear and the axis of the cutter, is determined by the helix angle of the teeth of the cutter. Thus for example, if the internal gear is a spur gear and if a cutter is employed having its external teeth extending at a degrees helix angle, the cutter and gear can be brought into proper mesh only with their axes crossed at an angle of 5 degrees.

The type of tool employed in the present invention may be an abrading tool, but preferably is in the form of a gear shaving cutter of the type disclosed in Drummond Patent 2,126,178 in which the teeth of the gearlike tool are provided with serrations or grooves extend ing up and down the sides of the teeth providing cutting edges. The cutting action between a gear shaving cutter of this type and the surface of the gear teeth engaged thereby is essentially due to a relative sliding action longitudinally of the teeth of the gear which is a function of the angle between the axes of the gear and tool. If this angle is zero, or in other words, if the axes of the gear and tool are parallel, no crossed axes slide is introduced but instead, the relative slippage between the teeth of the gear and the teeth of the cutter occupies planes perpendicular to the axes thereof. As a result of this it is desirable to provide a certain angle between the axes of the gear and cutter which is selected in accordance with the cutting action desired. Accordingly, it is not possible to select the angle between the axes of the gear and cutter in accordance with a crown formation or configuration required on the teeth of the work gear.

Even if it were possible by coincidence to obtain the desired cutting action and the required crowned configuration on the gear teeth by a particular crossed axes setting, it would be impossible to make minor changes in crossed axes setting to produce minor corrections or variations in the amount of crown and hence as a practical matter, it would not provide a satisfactory and efficient method of producing crowned internal gear teeth.

Also, it must be considered that to produce crowned internal gear teeth by providing a cutter in mesh with the teeth of the gear and by feeding it radially, initial contact between the teeth of the gear and cutter would be at one or both ends of the teeth of the cutter, unless the cutter were wider than the gear, in which case initial coneither case, the cutting action obtained would be undesirable. The most efiicient cutting action is obtained when initial contact is between intermediate portions of the gear and cutter and in which the cutting action may be extended continuously and progressively from the midpoint to either end of the teeth of the gear and employing a contact with the teeth of the cutter which in no case results in contact at the extreme end of the teeth of the cutter.

Applying these considerations to the crown finishing or shaving of the teeth of an internal gear, reference is now made to Figures 10-12. In Figure 10 there is a diagrammatic showing of an internal gear G having a tooth space 40 therein. A tool in the form of an external gear or pinion P is provided having teeth 42 designed to enter into tooth spaces 40 when the axes of the gear G and tool P are at a certain crossed axes relationship. If the teeth of the gear and pinion are unmodified from end to end, the contacting relationship between the teeth is as illustrated in Figure 10, this contact taking place at the corners of the teeth 42 of the tool.

In Figure 10 the shape of the tooth 42 as shown by the portion in section, may be considered as developed from a cylinder concentric with the axis of the gear G, and is of course grossly exaggerated for clarity.

Referring now to Figure 11 there is illustrated a cutter P having teeth 44 which are crowned or bowed longitudinally to have relatively thick portions intermediate their ends occupying the plane indicated at 46. When a tool such as the pinion P is meshed with the gear G the contact between the teeth of the pinion P and the teeth of the gear G is as illustrated in Figure 12 where the contact is limited to a zone substantially midway between the ends of the tool teeth 44 occupying and limited to a zone closely adjacent the plane 46.

Employing a pinion or small external gear as a tool in which the teeth are crowned sufficiently to produce contact at mid-portions thereof with unmodified teeth of the internal gear permits a gear finishing operation in which, by suitable adjustment, any desired crowned configuration may be imparted to the teeth of the internal gear and this may be done independently of a particular crossed axes setting which has been selected or arrived at in accordance with the most efficient cutting action.

Referring now to Figures 13 and 14 there is illustrated a simple apparatus for carrying out the present method. In this apparatus, as will subsequently appear, means are provided for supporting an internal gear for rotation, for angularly adjusting the internal gear about an axis extending diametrically therethrough, and for driving the gear in rotation. At the same time, means are provided for supporting a cutter in mesh with the internal gear at a crossed axes which may be selected entirely independently of any crowned configuration to be imparted to the teeth of the gear. For this purpose, means are provided for supporting the cutter for straight line reciprocation toward and away from the gear in a direction perpendicular to the axis of adjustment of the gear. At the same time, the means for supporting the cutter is designed for angular adjustment about an axis extending diametrically through the cutter and parallel to the axis of adjustment of the gear. With this construction relative traverse is accomplished in straight line relationship without adjustment. The particular crowned configuration to be imparted to the teeth of the internal gear may be determined by angular adjustment of the gear support, varying from zero crown when the gear is positioned with its axis parallel to the direction of relative traverse between the gear and cutter. Having set the gear in a position of angular adjustment to produce the desired traverse angle, the cutter is thereafter angular adjusted to the required crossed axes angle.

It may be mentioned at this time that the crossed axes angle will normally be between 2 and 20 degrees and the traverse angle may be any angle dependent upon the amount of crown to be imparted to the teeth of the gear.

In operation, either the gear member or the cutter member is driven in rotation and the other member rotated solely. by the meshed engagement between said members. In the present case means are illustrated for directly rotating the gear and for rotating the cutter through its meshed engagement with the gear. Speed of rotation is relatively high, as for example at a surface speed of approximately 500 feet per minute, and this is referred to herein as rotation of the gear and cutter at cutting speeds. On the other hand, relative traverse, which in the illustrated apparatus is accomplished by moving the cutter in a horizontal plane and in a direction selected to produce the required crown, is relatively slow on the order of 12 inch-es per minute.

Referring now to Figures 13 and 14 the gear shaving machine is illustrated as comprising a main frame 5d provided with a vertically extending column 52 having a forwardly extending portion 54 at its top. Mounted in the forwardly extending portion 54 is a motor indicated in dotted lines at 56 which is adapted to drive a work support 53 in rotation. The work support 58 is carried by a head 59 which is angularly adjustable about a vertical axis under the forwardly extending portion 54 and may be adjusted and locked in position by suitable clamping means such for example as bolts 59a extending into arcuate T-slots or the like. The driving connection intermediate the motor 56 and the rotary support 58 for the internal gear is such that the driving relation is maintained during angular adjustment of the work support about a vertical axis. The detailed mechanism for accomplishing this result forms no part of the present invention but suitable mechanism for this purpose is illustrated in Davis Patent 2,612,080. The machine comprises a knee 6% extending forwardly from the column 52 and located above a forwardly extending base portion 62. The knee is vertically adjustable by suitable mechanism such for example as a feed screw indicated at 64.

Located above the knee 6@ is a tool support or slide 66 on which is mount-ed a head 68 for supporting a gear shaving cutter 70. Intermediate the knee 6t and the tool slide 66 is a sandwich indicated generally at 72 comprising an upper member 74 and a lower member 76 provided with cooperating ways indicated generally at 78. The upper and lower sandwich elements 74 and 76 may be angularly adjusted in a horizontal plane with reference to the knee 6t) and element 66 and for this purpose are provided with arcuate T-slots indicated generally at 84 which may be associated with suitable bolts for locking the parts in adjusted position.

Suitable linkage 82, forming no part of the present invention but illustrated in the prior Davis patent, is provided to maintain the orientation of the tool slide 66 during angular adjustment of the sandwich 72.

The machine includes mechanism for effecting relative traverse between the upper member 74 and the lower member 76 in the direction of the ways 78. This means may comprise a suitable feed screw and nut as illustrated in detail in the prior Davis patent.

From the foregoing it will be apparent that by adjusting the sandwich 72 angularly, the cutter it? will be caused to traverse in any desired direction in a horizontal plane but will always remain with its axis extending parallel to the plane of the paper as viewed in Figure 13. At the same time the work support 58 may be angularly adjusted to any required angularity without affecting the drive relationship between it and its driving motor 56.

Accordingly, taking into account the fact that the orientation of the cutter is not disturbed during setting or operation of machine, the head carrying the work support 58 is angularly adjusted about a vertical axis tothe angle required to bring about proper meshing between the cutter 70 and an integral gear carried by the work support 58 as determined by the helix angle of the teeth of the work and cutter. This adjustment is dependent solely on the helix angle of the parts and is entirely independent of the direction of relative traverse which as described has not as yet been determined. As previously described, the cutter has its teeth crowned so as to limit contact between the teeth of the cutter and the teeth of the internal gear to a narrow zone adjacent the high point of the crown of the teeth of the cutter. In order to determine the amount of crown to be imparted to the teeth of the internal gear, the sandwich 72 is now adjusted to the proper angular setting. If the direction of the ways is brought into parallelism with the axis of the gear, traverse of the cutter will produce a shaving action between the teeth of the gear and cutter but will not produce a crown on the teeth. If however, the sandwich 72 is adjusted so that the ways extend at an angle to the axis of the gear, traverse of the slide 66 will produce crowned teeth and the amount of the crown can be controlled by setting a desired angle between the direction of the ways and the axis of the work.

As a result of the foregoing the crossed axes angle of the gear and cutter may be selected as desired for most eflicient cutting or for other considerations and the amount of crown may be predetermined by selecting the angularity between the direction of relative traverse and the axis of the cutter.

Thus, accurately controlled crowning may be produced in an operation characterized by the most efiicient cutting action.

The drawings and the foregoing specification constitute a description of the improved method of crown finishing the teeth of internal gears in such full, clear, concise and exact terms as to enable any person skilled in the art to practice the invention, the scope of which is indicated by the appended claims.

What I claim as my invention is:

1. The method of crown finishing the teeth of an internal gear member which comprises running a gear-like finishing tool member in mesh at cutting speed with the internal gear member with the axes ofsaid members crossed at an angle of between 2 degrees and 20 degrees, the tool member having its teeth crowned to an extent sufficient to limit the contact with the teeth of the gear member to narrow zones adjacent the thickest portion of the teeth of said tool member and producing a crowned configuration to the teeth of the gear member by eliecting relative traverse between said members in a plane parallel to the axes of both of said members and in a direction in such plane oblique to the axis of said gear member and selected in accordance with required crowned configuration.

2. The method defined in claim 1 in which the direction or traverse occupies a zone in said plane between the pro-,

jections of the axes of the gear and tool members thereon.

3. The method of producing a required crowned con figuration on the teeth of an internal gear member which comprises placing it in mesh with a cutting tool member in the form of an external pinion with the teeth of the tool member having a helix angle differing from that of the internal gear member by an amount to result in a crossed relationship between the axes of the members of between 2 degrees and 20 degrees, the teeth of said tool member being crowned sufficiently to limit contact with the teeth of said gear member to a narrow zone adjacent the diameter of the tool member intersecting the high point of the crown, driving one of said members in rotation at cutting speed and driving the other member solely through the meshing relation of said members, and rela tively traversing said members in a plane parallel to the axes of both of said members and in a direction in said plane oblique to the axis of said gear member and selected independently of the helix angles of the crossed axes angle of said members to produce the required crowned configuration on the teeth of said gear member.

4. The method defined in claim 3 in which the direction of traverse occupies a zone in said plane between the projections of the axes of the gear and tool members thereon.

References Cited in the file of this patent UNITED STATES PATENTS Miller Ian. 14, Miller Jan. 14, Miller Ian. 14, Miller Apr. 14,

Miller July 24, 

